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<html lang="en">
<head>
    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <p>one</p>
    </div>
    <script>
        var app = document.getElementById("app");
        var p = document.createElement("p");
        p.innerHTML = "前面";
        app.prepend(p);
    </script>
</body>
</html>